Alongside the inevitabilities of long-term interest rates picking up and inflation firming, one of the most obvious things that was going to happen over the course of this year was a narrowing of profit margins. So much for that.

Indeed, with third-quarter earnings advancing at around twice the pace of a sales gain of just 5.3%, profits as a share of revenue for companies in the S&P 500 look to now stand at 10.1%. That is the widest profit margin in the 22 years of data S&P Dow Jones Indices has on hand. A...